EFFECTS OF LOW-TEMPERATURE, HIGH SALINITY AND EXOGENOUS ABA ON THE SYNTHESIS OF 2 CHLOROPLASTIC DROUGHT-INDUCED PROTEINS IN SOLANUM-TUBEROSUM

Two chloroplastic proteins of 32 and 34 kDa were previously shown to b e substantially synthesized in response to a progressive water deficit in whole Solanum tuberosum plants (G. Pruvot, S. Currie, N. Gault, G. Peltier and P. Rey, unpublished data; G. Pruvot, S. Cuine, G. Peltier and P. Rey. 1996. Planta 198: 471-479). These chloroplastic drought-i nduced stress proteins, named CDSP 32 and CDSP 34, accumulated in the stroma and in the thylakoids, respectively. In this study, we investig ated the effects of low temperature and high salinity on the synthesis of the CDSP proteins. Whereas the CDSP 32 synthesis was not modified in response to a cold treatment, an increased synthesis of CDSP 32 was observed in salt-stressed plants, resulting in accumulation of the pr otein. The thylakoid CDSP 34 protein exhibited enhanced synthesis and substantial accumulation in response to cold and high salinity. A sign ificant increase in the leaf abscisic acid content (at least 2.5-fold) was measured in plants subjected to water deficit, high salinity or l ow temperature. The contribution of ABA to the synthesis of the two pr oteins was investigated by spraying well-watered plants with a 100 mu M ABA solution for 15 days. This treatment resulted in a 15-fold incre ase in the leaf ABA content. Whereas synthesis of the CDSP 32 protein was not affected by exogenous ABA, synthesis of the CDSP 34 protein wa s substantially enhanced. Based on these results, we conclude that ABA likely mediates the increased synthesis of CDSP 34 upon drought, low temperature and high salinity and suggest that another signal, likely related to high osmolarity, is involved in the induction of CDSP 32 sy nthesis.